Remedy some GCC warnings

The `#ifdef SMALLTABLES` change eliminates the unused variable warning and the array size changes fix the arrays to be the right size for the call to `sc25519_window4`, and thus silences the `-Wstringop-overflow=` warning group in GCC. These changes should not at all affect the result of the operations, as the last 19 extra bytes in the array will remain unused.

Author: Jeffrey Ryan

crypto_sign/ed25519/amd64-64-24k/ge25519_scalarmult_base.c

@@ -12,11 +12,13 @@ static const ge25519_niels ge25519_base_multiples_niels[] = {
 };
 
 /* d */
+#ifdef SMALLTABLES
 static const fe25519 ecd = {{0x75EB4DCA135978A3, 0x00700A4D4141D8AB, 0x8CC740797779E898, 0x52036CEE2B6FFE73}};
+#endif
 
 void ge25519_scalarmult_base(ge25519_p3 *r, const sc25519 *s)
 {
-  signed char b[64];
+  signed char b[85];
   int i;
   ge25519_niels t;
   fe25519 d;

src/amd64/amd64.c.inc

@@ -109,7 +109,7 @@ static void negate(ge25519* out)
 // similar to loops in existing implementation, but uses dynamic table instead of fixed `G`.
 static void scalarmult_p1p1(ge25519_p1p1* r, ge25519_pniels const* base, char const* sec)
 {
-  signed char b[64];
+  signed char b[85];
   ge25519_pniels t;
   ge25519_p3 tp3;